I am also lvl 5. I train the same every day, regardless of a game or not. I dont power train. I also dont go below 80% unless I have 5-6 three hour intervals for resting, where I will go down to 70%, but thats as far as I go so I dont tempt the injury gods.
Only the power trainers would be able to tell you how low you can go before you hit serious injuries.
As far as I know, there is an infinite amount of levels...that is, there is no TOP level. It just keeps going as long as people keep playing and paying.
Some guys are close to 30 seasons. Do we know of any that are more than 30?